I used one of the numbers posted in this forum to call Citi after my invite for double cash Citi card app was denied. The rep explained that since I applied Costco business card, the pulled the EQ and denied based on less credit history I had (I only have two years history and only one credit card). I tried AA card from Citi as I got invite in mail. And then double cash twice.
The rep explained that since I pulled my trigger with Costco card, they have my application in system and my subsequent applications are denied. I need to wait for three months before I apply again. Any application they will receive meanwhile will be denied immediately.